Cannot change App store country/Region for family members.

We have recently moved from UK to Australia and are looking at moving our Apple Accounts from UK to Aus.

We are all running ios/ipadOS/MacOS 14

We have a family account set up (2 adults 2 kids.)

Us 2 adults have managed to migrate our icloud accounts and the associated App store to Australian ones.

However the 2 children have been able to change their icloud accounts to Australia, however we do not seem to be able to change their App store to the australian app store and in turn they cannot now download any new apps to their iPads.

We try to change their shipping address to Australia but country region cannot be updated.

What is the correct process for migrating a family icloud and app store from one geography to another as it seems overly complicated.

Thanks